Technical Abstract:
The production of fruity fermented off-flavor due to high temperature curing is a significant problem in peanuts. Because peanut flowering is indeterminate, a range of maturity stages is present at harvest. Immature peanuts are associated with increased fruity fermented off-flavor, and upon roasting, in any grade size, acquire a darker color and have lower flavor potential.
The objective of this study was to determine the effectiveness of a novel application of machine color sorting to remove fruity fermented off-flavor and improve flavor and shelf-life of roasted peanuts by removal of darker (immature) peanuts.
Fruity fermented and non-fruity fermented runner-type peanut lots (65 kg each) were roasted at 174 C ± 2 C, blanched, and subdivided into 3 lots. Each sub-lot was color sorted using a Sortex color sorter (model #3201). The color sorter was adjusted to remove ca. 5, 12 and 20% of the darkest peanuts, which had resultant Hunter L colors of ca. 40, 42 and 44. The lighter, color-sorted peanuts (mature) were stored at 30 C and samples were evaluated at 0, 1, 2, 4, 8, and 12 weeks. Peroxide value (PV), oxidative stability index (OSI), descriptive sensory analysis, single-seed roast color, moisture, lipids, carbohydrates, fatty acids and free fatty acids (FFA) were determined for all samples.
Total oil content was similar in all samples. The darker (immature) peanuts had higher concentrations of unsaturated fatty acids, FFA and carbohydrates. No significant differences were found in PV and OSI in the light color-sorted (mature) samples during storage suggesting that color sorting did not enhance shelf-life. Descriptive sensory analysis showed that fruity fermented off-flavor decreased with successively higher percentage removal of darker-roasted, immature peanuts.
The reduction of fruity fermented off-flavor in roasted peanuts by machine color sorting may be of significant economic value to the peanut industry.